Warp knit fabric



United States Patent Office 3,041,851 Patented July 3, 1962 3,041,861 WARP KNIT FABRL'C Robert Allen Kasey, Jr., Wilmington, Del., assignor to E. l. du Pont de Nemours and Company, Wilmington, Dei., a corporation of Delaware Fiied Apr. 22, 1955, Ser. No. 730,194 1 Claim. (Cl. 66-195) This invention relates to improvements in warp knit fabrics and more particularly to a novel process Ifor preparing such fabrics with improved covering power.

Prior work in this field has employed yarns having differeutial fiber shrinkage within the same yarn, for example, composite yarns made by plying low shrinkage with high shrinkage yarns, winch are then knitted (with the same yarn in both bars) and finished under relaxed conditions to allow shrinkage of the high shrinkage component and thereby yield a fabric having slightly improved cover. This is a costly process involving yarns of relatively low total denier. Work has also been carried out employing alternating ends of high and low shrinkage yarns for obtaining different puckered effects.

One object of this invention -is to provide a process for significantly increasing the covering power of warp knit fabrics, especially the covering power of the transmitted light type. Another object is to provide a method of making tricot fabrics with superior covering power at equivalent weight to the fabrics made heretofore, as ywell as lighter weight fabrics with the same covering power as those already known` Other objects will be apparent lfrom the description of the invention given below.

According to this invention there are provided novel knitted fabrics by feeding at the top front bar of a knitting machine a relatively low shrinkage yarn having a retractability of 30%, and by feeding at the bottom back bar of said machine a relatively high shrinkage yarn having a retractability of 3-40%, the differential in retractability (i.e., residual shrinkage) between the two yarns being at least 3 and relaxing the resulting knitted fabric to allow all of said retractable yarn components to shrink. Retractability as used herein refers to a lengthwise shortening of the fiber or filament, whether occurring by means of crimping, shrinkage, or other means.

The invention will be more easily understood by reference to the drawings:

FIGURE 1 is a loop diagram of a conventional prior art greige or finished tricot fabric in which the yarns of the top bar and yarns of the bottom bar have the same shrinkage. The yarns lay on top of one another, thus giving a thick fabric which has poor transmitted light cover because of the relatively large holes through which light can pass.

FIGURE 2 is the loop diagram of the back of greige tricot fabric (Jersey stitch) of this invention. Yarn loops A, C, and -E in RIGURE 2 are loops formed by bottom guide bar yarn which has relatively high shrinkage and yarn loops B, D, and F are loops formed lby top guide bar yarn which has relatively low shrinkage (more than 3% less than high shrinkage yarn). Loops (A, C, and E.) formed by the `bottom guide batare on top of the loops B, D, and F for-med by the top guide bar.

FIGURE 3 shows the loop diagram structure of the back of the finished fabric after scouring. As can be seen in FIGURE 3, the yarn forming the loops A, C, and E shrinks more than the yarn from the top guide bar forming the loops B, D, and F. So loops A, C, and E are shorter than loops B, D, and F. As the loop A shrinks, it pulls the holding loops C and D downward, and loop C pulls the holding loops E and F downward. The result of this differential shrinkage and the tightening up of the loops formed by the bottom guide bar is that low shrinkage loops (B, D, and F) are larger than high shrinkage loops A, C, and E. This structure gives a more efficient use of the yarn in that the yarns are not superimposed on one another, thereby providing much smaller holes through which light can pass and much improved transmitted light cover.

rI'he fabrics may be knitted 'from any lament or spun (i.e., staple) yarns, or a blend or filament and staple, preferably employing synthetic -filamentary material to confer high shrinkage to the yarn fed to the bottom bar. Examples of such synthetic filamentary materials include those fibers and filaments made from polyamides such as polyhexamethylene adipamide and polycaproamide, polyesters such as polyethylene terephthalate, acrylonitrile polymers and copolymers, vinyl chloride polymers and copolymers, vinylidene chloride polymers and copolymers, polyethylene, tetrafiuoroetlhylene polymers and copolymers, cellulose derivatives such as regenerated cellulose and cellulose acetate, and any other fiber which can be prepared so that it has at least 3% and preferably at least 10% residual lengthwise shrinkage. These synthetic fibers having the requisite residual shrinkage may be prepared by known methods, such as described -in U.S. Patents 2,604,689 to Hebeler, 2,758,908 to Kolb, and 2,515,834 to Nicoll. The low shrinkage yarn may be made from either synthetic or natural filamentary material including any of those mentioned above as well as wool, cotton, silk, and the like. At least a 3% differential in shrinkage between the two yarns is required to obtain significant improvements in the covering power of tricot fabrics made in accordance with this invention. IHowever, it is preferred to employ low and high shrinkage yarns having at least 10% differential in shrinkage and greater, since the higher the shrinkage differential between the two yarns, the better the improvement in covering power of the fabric.

'Ilhe terms high shrinkage and low shrinkage refer to residual shrinkage which is defined as the percentage loss in length when a yarn undergoes when placed in boiling water at atmospheric pressure for 5 minutes. The high and low shrinkage ya-rns are high and low relative to each other, there being a differential between the two of at least 3% residual shrinkage.

lt is preferred in this invention that the yarn fed to the bottom bar should be composed entirely of high shrinkage filamentary material 4and the yarn fed to the top bar entirely of low shrinkage filamentary material. However, for some uses fabrics may be knit from other combinations so long as the differential shrinkage between top and bottom bar yarns is atleast 3%. Thus, a fabric may be knitted from a spun yarn on the bottom bar composed of a fiber blend of high and low shrinkage fibers and a spun yarn on the top bar composed entirely of low shrinkage fibers, with a differential shrinkage between the two yarns of 10%. Another fabric may be knitted by feeding on the bottom bar a spun yarn composed entirely of high shrinkage fibers and on the top bar a spun yarn composed of a blend of low and high shrinkage fibers such that the shrinkage of the yarn on the bottom bar is greater than that of the yarn on the top bar by at least 3%. Also, a fabric may be knitted from a high shrinkage filament yarn on the bottom bar and a low shrinkage spun yarn on the top bar, or from a high shrink-age spun yarn on the bottom bar and a low shrinkage filament yarn on `the top bar, provided the differential shrinkage between the two yarns is at least 3% One surprising aspect of the present invention resides in the observation that the improved covering power of warp knit fabrics is not realized if the high shrinkage yarn is fed to the top bar and the low shrinkage yarn to the bottom bar of the knitting machine. Only if these yarns are fed in the proper sequence will the improvement in cover be realized.

The warp knit fabrics of this invention may be prepared using any of the standard Warp knitting machines available. Thus, tricot and Simplex knitting machines may be employed using two, three, or more bars with different gauges (eg, 26 gauge, 28 gauge, 32 gauge, or coarser). Also, Raschel knitting machines may be used having one or two needle beds with two or more guide bars. However, the fabrics must be knitted in a more open construction than is normally employed. After knitting, the fabrics will then be subjected to finishing treatments which will allow the shrink-able lamentary materials to shrink in order to obtain the improved cover. The shrinkage may take place in one or more operations which are normally used for finishing fabrics such as heating, scouring, dyeing, bleaching, tentering, washing, and the like. After shrinkage, the fabric may be framed out to the desired dimensions.

Various known methods may be used for shrinking the knitted fabrics containing residual shrinkage iilamentary material. yFor example, fabrics containing retractable polyamide yarns may be shrunk by treatment with phenolic compounds or dilute nitric acid. Fabrics containing retractable acrylonitrile polymer yarns may be shrunk by treatment with steam, phenolic compounds, or solutions of ethylene carbonate or propylene carbonate. Fabrics containing retractable polyethylene terephthalate yarns may be shrunk by treatment with steam, dry heat, hot water, or methylene chloride. Retractable regenerated cellulose yarns may be shrunk in anhydrous liquid ammonia, whereas retractable cellulose acetate yarns may be shrunk in aqueous acetone solutions.

The covering power of the warp knit fabrics described in the specification is measured in terms of the percent of normal incident white light passing through the fabric. This is called the amount of transmitted light (designated herein as percent It) and is determined using apparatus consisting of a light source (incandescent lamp) with constant voltage supply; a sample holder mounted l2 inches from the light source; a Weston Photronic cell (Model 594-RR) mounted 6 inches beyond the fabric, -all enclosed in a black velvet-lined box. rThe output of the photoelectric cell is measured directly on a microammeter and is calibrated with a series of standard filters.

An important advantage of the present invention is the provision of a process for preparing tricot fabrics having a higher cover/weight ratio than is possible in fabrics made using conventional techniques. This improved covering power results from a different structure of the final fabric wherein the individual filaments and yarn components are much closer together and, therefore, intercept more light than in tricot fabrics available in the past. This difference in fabric structure allows more eicient use of the yarns in blocking the passage of light through the fabric. The invention also permits the manufacture of lighter weight tricot fabrics having cov- @ring power equal to that of heavier conventional fabrics, which means in turn lower cost and more desirable fabrics may be prepared. The tricot fabrics made by the novel techniques of this invention may be used to produce superior slips, gowns, lingerie, and other under-garment fabrics as well as improved dresses, blouses, and outer- Wear fabrics.

The following examples illustrate specific embodiments of this invention. All parts and percentages are by Weight unless otherwise specified. All tricot fabrics described in the examples were made on -a tricot knitting machine. Each yarn was made from continuous tilaments, the first number indicating the denier of each filament, the next number the number of filaments, the next number the number of turns per inch and in which direction, and the last number the total denier of the yarn. All nylon filaments used in the examples were made from polyhexamethylene adipamide.

Example l Yarn:

(#1) 40-13-l/2Z-680 nylon (9-10% shrinkage).

Coning:

60 cones made of yarn I# 1.

60 cones made of yarn #2.

Warping:

(it 1) 10-2 section beams made of yarn #l for bottom bar of Aveco 21" tricot machine.

(#2) lll-2 section beams made of yarn #2 for top bar of Aveco 21" tricot machine.

Knitting:

(l) Warp of yarn #l (high shrinkage) is used on bottom bar of 21" Aveco tricot.

(2) Warp of yarn #2 (low shrinkage) is used on top bar of same machine.

A normal Jersey knitting stitch is used:

Top bar 2-3, 10.

Bottom bar 1-0, l-2.

Open stitch and normal knit ratio are used. In this case:

Quality- 9" (9" fabric/480 stitches on machine). Top yarn runner-64" (64 yarn knit/ 480 courses). Bottom yarn runner-44 (44" yarn knit/ 480 courses).

Knit ratio-1.45.

Greige construction-56 courses x 44 wales/in.

Finishing:

Fabric is scoured at the boil relaxed for 1/2 hour using an anionic dispersing agent (Duponol RA).

Scoured construction-60 x 47. Percent Vshrinkage-1367?: in length, 10% in width.

Fabric is heat-set at 420 F. for 30 seconds under slight tension. Fabric is then bleached using Textone and acetic acid, rinsed, air dried, and pressed.

Finished construction-58 x 48. Finished weight=3.24 oz./yd.2. It=5.5%.

Example 2 Yarn is the same as in Example l except that yarn #l (high shrinkage) is fed at the top bar, and yarn #2 (low shrinkage) is fed at the bottom bar. Warping, knitting, and finishing conditions are the same as in Example l. Finished fabric weight=3.l4 oz./yd.2; finished fabric 1t=12.2%.

This fabric provides much inferior cover than fabric knit according to procedure in Example 1.

Example 3 A good quality commercial nylon filament tricot slip is characterized as follows:

A fabric knit of Example l with relatively low shrinkage yarn in the top bar and relatively high shrinkage yarn in the bottom bar has much improved cover, readily discernible by subjective or objective tests, over this commercial fabric.

Example 4 Yarn:

40-27-0 polyethylene terephthalate larnent (control) (l0% shrinkage). Coning:

60 cones. Warping:

20- section beams l0 each for top and bottom bar of 2l Aveco tricot machine. Knitting:

Both bars containing control yarn.

Stitch:

Top bar 2-3, 1-0. Bottom bar 1-0, 1-2. Quality 7 (7l fabric per 480 courses). Top runner 62". Bottom runner 431/2". Knit ratio 1.42. Greige construction 65 courses 37 wales. Finishing:

Fabric scoured at the boil for 1/z hr. in relaxed condition, 10% anionic dispersing agent (Duponol RA). Scoured construction-66 X 48. Percent shrinkage-5% length, 25% width. Fabric heat-set at 420 F. for 30 seconds to construction of 56 X 48. Bleached-Textone and nitric acid at 190 F. Finished construction-5 6 X 52. Finished Weight=3.18 oz./yd.2. It: 10.6%.

Example 5 Yarn:

(#1) 40-27-0 polyethylene terephthalate lament (1% shrinkage-steam relaxed in skein form). (#2) 4027-0 polyethylene terephthalate lament shrinkage). Coning:

60 cones of yarn #1. 60 cones of yarn #2. Warping:

10-2" section beams of yarn #1. 10- section beams of yarn #2. Knitting:

Top bar yarn #l (low shrinkage). Bottom bar yarn #2 (high shrinkage). Stitch:

Top bar 2-3, 1-0. Bottom bar 1-0, 1-2. Quality 9". Top runner 64". -Bottom runner 44". Knit ratio 1.45. Finishing:

Fabric scoured at boil for 1/2 br. in relaxed condition with 10% anionic dispersing agent (Dupono1 RA). Scoured construction-l X 46. Fabric heat-set 420 F. for 30 seconds to construction of 5S x 48. Fabric bleached Textone and nitric acid 190 F. Finished construction-55 x 49. Finished weight=3.31 oz./yd.2. It=4.2%.

This fabric has much improved cover over the control fabric of Example 4.

Example 6 Yam-reversed in knitting machine:

Top bar-yarn #2 (high shrinkage). Bottom bar-yarn #l (low shrinkage). Stitch:

Top bar 2-3, 1-0. Bottom bar l-O, 1-2. Quality 9". Top runner 64". Bottom runner 44". Knit ratio 1.45. Fnshing-identica1 with Example 5:

Scoured construction-5 6 X 48. Heat-set construction- 56 X 48 (relaxed). Finished construction- 56 X 49. Finished weight-3.37 oZ./yd.2. It-10.2%.

This fabric is no better than the control of Example 4 in cover.

The claimed invention:

A greige tricot fabric knitted with a normal Jersey stitch from two 27 filament zero twist yarns composed of polyethylene terephthalate 40 denier continuous lilaments exhibiting residual shrinkage when relaxed in boiling Water at atmospheric pressure for 5 minutes, one yarn having 1% shrinkage and the other having 10% shrinkage, the knit of the fabric being such that, when viewed from the back, the loops of 10% shrinkage yarn are on top of the loops of 1% shrinkage yarn, the dilerential shrinkage of the two yarns providing a fabric of improved covering power after the fabric is finished by scouring at boil for 1/2 hour in relaxed condition, the light transmission when so finished being approximately 40% of the light transmission of otherwise corresponding fabric wherein the yarns are of equal shrinkage.

References Cited in the le of this patent UNITED STATES PATENTS 2,108,735 Wirth Feb. 15, 1938 2,147,169 Mendel et al Feb. 14, 1939 2,403,793 Feinstein July 9, 1946 2,409,026 Feinstein Oct. 8, 1946 2,608,078 Anderson Aug. 26, 1952 2,789,340 Cresswell Apr. 23, 1957 FOREIGN PATENTS 657,630 GermanyY Mar. 9, 1938 644,804 Great Britain Oct. 18, 0 

